The present invention relates to pavement breakers in which a cutting or crushing tool is mounted to the output end of a resonantly driven beam, and in particular to the penetration tool used on such devices.
A pavement breaker of the type utilized in connection with the present invention is illustrated in my above-referenced U.S. Pat. No. 4,340,255. The pavement breaker includes a mobile carrier vehicle which rides over the pavement to be broken. A resonant beam having input and output antinodes at its ends and a pair of stationery nodes intermediate its ends is mounted to the vehicle at the nodes. The beam is excited to near its resonant frequency, and a penetrating tool depending from the output end of the beam breaks the pavement underlying the vehicle. The tool may have a relatively narrow striking surface to essentially slice through or cut the underlying pavement, or a wider surface to achieve a pulverizing or crushing action.
The cross-referenced application describes an improvement in the penetrating tool used in the pavement breaker of the type disclosed in the patent. This tool includes a flat bottom surface, and inclined flanges forward and rear. The forward flange strikes the pavement at a relatively small closing angle, between about 6.degree. and 18.degree., to initially break the pavement. The flat bottom further crushes the pieces broken off by the forward flange. The rear flange is provided so that the tool can be reversed when the flange in use becomes worn.
While the tool described in the cross-referenced application has been found to be quite useful, the required force to break the pavement has been found to increase as the stroke of the tool proceeds toward completion. It has been discovered that this results from the fact that the closing angle, defined as the angle between the direction of motion of the portion of the tool striking the pavement and the inclination of the flange at that point, increases throughout the stroke of the tool. The tool essentially pivots about the adjacent node of the resonant beam, and the increased distance between this node position and the portion of tool striking the pavement increases throughout the stroke of the tool, thus increasing the closing angle.
The system must accommodate the maximum force encountered, which will occur at the end of the stroke in the tool described above. As a result a system with such a tool will operate below its optimum at intermediate portions of the stroke. This system is somewhat unstable because the reaction forces will vary with the depth of penetration of the tool and also with irregularities in the surface being broken.